Due to the shortage of energy and the greenhouse effect of the earth, more and more lamp sources use solar energy as power source. This is because solar energy is a clean energy and can be got easily.
The prior art solar lamp has a battery set installed at a lower side of the lamp rod. It is heavy and is easily theft. Furthermore, each battery set serves for only one light source. In cloudy day, the sunlight is insufficient. The power storage in the battery set is also insufficient. It cannot provide sufficient illumination to the light source. As a result, some light sources can not light up or light up only a short time.
There are some patents related to the power control of the solar lamp, for example, in U.S. Pat. No. 6,909,245, “Ballast circuit for control of lamp power” in that a ballast circuit for operating a discharge lamp is equipped with a control loop for controlling the power consumed by the lamp. A first circuit part is coupled to the discharge lamp and to input terminals for connection to a source of supply voltage for the ballast circuit. The first circuit part is coupled to the input terminals to supply lamp current from the supply voltage. The control loop includes a second circuit part coupled to the first circuit to generate a first signal that represents a desired value of lamp power. A third circuit part is coupled to the input terminals for generating a second signal that depends on the amplitude of the supply voltage. A fourth circuit part has an input coupled to the third circuit part and an output coupled to an input of the second circuit part for adjusting the value of the first signal dependent upon the second signal. The power consumed by the lamp is decreased when the amplitude of the supply voltage decreases. Too high currents in the ballast circuit are thereby prevented.
Furthermore, in U.S. Pat. No. 6,031,211, “Radiation-sensitive control circuit for driving lamp at various power levels”, an exposure system is disclosed, which comprises a lamp, a power supply for directing said lamp at an idle level which optimizes the life of said lamp, means for driving light from said lamp through a light path to an exposure plane, exposure means for controlling the exposure period during which light at a preselected level from said lamp reaches the exposure plane, light detector means in the light path coordinated with said exposure means for detecting the light intensity from said lamp during the exposure period, and a control circuit connected to said power supply, said control circuit being responsive to said light detector for adjusting said power supply to provide the preselected level of light output from said lamp during the exposure period, said control circuit including means for reducing the power to said lamp below the idle level, means for increasing the power to said lamp above the idle level, and a summing circuit connected to said light detector for producing an output to cause a reduction or an increase in the power to said lamp.
However, these prior art are only related to power control for only one lamp. No prior art provides a system for controlling the power of many lamps, this is especially important for street lamps. Generally, a load has many street lamps, especially in a large load, such as a super high way which is arranged several hundreds or thousands lamps. However the prior art power control of the lamp is individual, that is the power control can not be performed by adjusting the power levels of several light sources.
Furthermore, it is known that if power stored in the battery set is full or exhausts completely through a longer time, the performance of the street lamp will deteriorate and thus the lifetime of the street lamp is shortened.